1 North Shore University Hospital, Manhassett, NY, USA
2 Icahn School of Medicine at Mount Sinai, New York, NY, USA
Direct arterial pressure monitoring is recommended for all ICU patients with hemodynamic instability who require inotropic or vasopressor medications as well as significant ventilatory deficits. This allows for continuous monitoring of blood pressure as well as access to the arterial circulation for the measurement of arterial oxygenation and frequent blood sampling.
As the pulse moves peripherally, the pressure waveform is distorted with higher systolic pressure and pulse pressure (Figure 11.1).
Locations for placement
Radial artery: common site of cannulation. Check collateral flow of ulnar artery with the Allen’s test, which has low reliability.
Brachial artery: located in antecubital fossa, lack of collateral circulation, median nerve injury possible.
Axillary artery: can cause axillary nerve damage from hematoma or traumatic cannulation.
Femoral artery: prone to pseudoaneuryms and atheroma formation.
Dorsalis pedis and posterior tibial arteries: most distorted waveforms.
Deficiencies of collateral circulation (e.g. Raynaud’s phenomenon).
Multiple proprietary systems have developed algorithms for estimating cardiac output from the arterial waveform. Arterial pulse contour analysis can evaluate stroke volume to calculate cardiac output and examine stroke volume variation to assess fluid responsiveness.
Characteristics of the arterial pressure waveform are affected by changes in vascular compliance, aortic impedance, and peripheral arterial resistance, limiting the accuracy and utility of this class of monitors.
Pulse contour analysis
The principle is based on the hypothesis that stroke volume is proportional to the area under the curve of the systolic segment of an arterial waveform.
PiCCO system (Pulsion Medical Systems)
Pulse contour cardiac output (PiCCO) requires the insertion of a central venous catheter and a thermodilution arterial line.
It provides hemodynamic monitoring by combining pulse contour analysis and a transpulmonary thermodilution technique to provide a continuous display of PiCCO cardiac index (L/min/m2) and stroke volume (mL/kg).
Calibration of the PiCCO to more accurate transpulmonary thermodilution cardiac output measurements needs to be repeated every 8 hours, or more frequently if the patient is hemodynamically unstable.
Additional data derived from the PiCCO system include:
Extravascular lung water index (mL/kg).
Global end‐diastolic volume (measure of cardiac preload in mL/m2).
Systemic vascular resistance index (dyn·s/cm5/m2).
Stroke volume variation (%).
FloTrac™ system (Edwards Lifesciences)
Requires an arterial line.
Uses pulse contour analysis based on an algorithm to provide continuous cardiac output, stroke volume, and stroke volume variation in real time.
Provides an estimate of cardiac output using the standard deviation of the arterial pulse pressure around the mean arterial pressure and a conversion factor.
Calibration is not required.
Pulse power analysis
Lithium dilution cardiac output (LiDCO) requires a peripheral or central arterial line.
Uses pulse power analysis rather than pulse contour analysis. The algorithm is based on the assumption that the net power change in the system in a heartbeat is the difference between the amount of blood entering the system, the stroke volume, and the amount of blood flowing out peripherally.
Requires calibration using transpulmonary lithium indicator dilution technique via a peripheral venous line. It is not as accurate when the patient is receiving lithium or certain neuromuscular‐blocking agents.
CVP is measured via a central line at the level of the right atrium or vena cava. It is equal to the right ventricular end‐diastolic pressure.
CVP can be used to determine preload, the filling pressure of the heart. It has been used to estimate whether a patient is adequately resuscitated as well as helping to assess right ventricular function.
As the heart beats, a CVP waveform is produced. There are three waves and two descents (Table 11.1 and Figure 11.2).
Controversy regarding the utility of CVP monitoring
Use of CVP to guide fluid management has been heavily debated. CVP is not useful as a static measurement. Trending the CVP can be useful to determine a patient’s response to a fluid challenge.
Useful measurements depend on proper calibration, normal pulmonary resistance, and right heart function.
Pulmonary artery catheter monitoring
Swan and Ganz first described the pulmonary artery catheter (PAC) in 1970 and it was widely used in the 1980s. However, as more trials were published in the 1990s and 2000s, its popularity declined.
Connors et al. published a prospective randomized trial in 1996 finding an increased cost, length of stay, and mortality in critically ill patients with a PAC.
The Fluid and Catheter Treatment Trial compared mortality, ventilator‐free days, and ICU length of stay among patients with acute lung injury and found no significant benefit to PAC in PAC‐directed resuscitation. The use of PAC resulted in no difference in LOS in the ICU or mortality.
The PAC requires placement of a balloon‐tipped catheter into the right atrium, across the tricuspid valve, into the right ventricle, and across the pulmonary valve, until it is ‘wedged’ into a pulmonary artery. At each anatomic location different pressure waveform profiles will be seen (Figure 11.3).
Acute MI with progressive hypotension or suspected mechanical complications.
Ultrasound echocardiography is an operator‐dependent hemodynamic assessment, which is a quick and non‐invasive measurement tool. Its effectiveness has not yet been proven in randomized clinical trials.
Cardiac function and anatomy can be assessed using five standard views (Table 11.2).
Stroke volume can be estimated with echocardiography:
SV = π × R2 × velocity time interval (VTI) of the left ventricular outflow tract (LVOT) (R= radius of LVOT in cm).
Parasternal long axis view is used to measure diameter of the LVOT.
Apical five chamber view is used to measure the VTI with pulsed Doppler.
Routine measurements of the size of the IVC and collapsibility with respiration can be used to estimate right atrial pressure (RAP) and fluid responsiveness in patients via the subcostal view on echocardiography.
Size ≤2.1 cm, collapses >50% during inspiration = RAP 0–5 mmHg.
Size >2.1 cm, collapses >50% during inspiration = RAP 5–10 mmHg.
Size >2.1 cm, collapses <50% during inspiration = RAP 10–20 mmHg.
Porter TR, et al. Guidelines for the use of echocardiography as a monitor for therapeutic intervention in adults: a report from the American Society of Echocardiography. J Am Soc Echocardiogr 2015; 28:40–56.
Weiner R, Ryan E, Yohannes‐Tomicich J. Arterial line monitoring and placement. In: Oropello JM, Kvetan V, Pastores SM (eds) Critical Care. New York: McGraw‐Hill, 2017, pp. 1085–92.
Yunen RA, Oropello JM. Pulmonary artery catheterization. In: Oropello JM, Kvetan V, Pastores SM (eds) Critical Care. New York: McGraw‐Hill, 2017, pp. 1245–61.